This invention relates to a drive unit for transferring rotary force and motion from outside of a hermetically sealed unit to within the sealed unit without the use of lip seals or other shaft seals. Such hermetically sealed drives are used primarily for adjusting sealed instruments on aircraft as well as in space and other applications.
A variety of techniques have been developed in the prior art in order to transfer force and motion across sealed barriers. One technique alluded to above is the use of a lip seal against a rotating shaft. Sealing is effected by the tightness of a seal as it rubs against a polished shaft, as well as by lubricant oil. Typically, these seals are used in automotive air conditioner drives, and are ideal for environments in which lubricant oil may be used for sealing purposes and in which the sealed body is pressurized with respect to the atmosphere or external environment. While such a seal can transfer a large amount of force, usually limited only by the strength of the journalled shaft itself, a certain amount of fluid loss must be tolerated, as, for example, in the above example of automotive air conditioners, where fluid must be added every five to ten years along with an oil charge. Thus, the lip shaft is not a true hermetic seal.
In many cases, it is possible to provide for a transfer of movement by electrical or magnetic means. A typical system would include a matched pair of rotary magnets located on opposite sides of a sealed barrier so that the movement of one magnet effects a corresponding change in the position of the other magnet. Similarly, electrical circuits can be used to translate motion across a hermetically sealed barrier. In either case, such a drive tends to increase the weight of the equipment and tends to allow slippage. Moreover, such a drive is not positive in that slippage may occur. Especially when fine adjustments are made, an electrical or magnetic drive would tend to be difficult to accurately hold in position. Thus, in many cases, a breaking mechanism is required, thereby increasing the complexity and weight of the device.
One technique used to mechanically transfer force across a barrier includes a stick having a ball at one end. The stick is pivoted at a center section so as to cause the ball to move in a circular path. By pressing the ball against a wobble plate, the pivoting stick is able to transfer rotary force across a barrier, usually located near the pivot point. Torque in this arrangement is limited to the size of the shaft. Additionally, the ball has to be constructed so as not to excessively wear when the stick is being pivoted.
In another device, a thin walled gear is deformed by a shell so as to cause it to take a more-or-less elliptical profile. By moving the shell, the ellipital profile rotates with respect to the teeth on the gear, thereby allowing a rotation of the shell to drive another gear in a reverse direction. This system requires a large amount of force to deform the thin walled gear, as well as requiring a large amount of movement in order to effect a small change in adjustment within the hermetically sealed container.
It is the object of the invention to provide a more direct means for transferring rotary force and motion across a hermetically sealed barrier. It is a further object to provide a means for transferring force and rotary motion across a sealed barrier, the means being light in weight and not permitting significant amounts of slippage over the lifetime of the device. It is a further object of the invention to provide a means for positively transferring rotary motion across a hermetically sealed barrier, even though large amounts of force may be required to effect such motion.